Health officials across Africa are currently engaged in the least enviable game of epidemiological detective work imaginable: figuring out exactly how Nigeria's first Ebola patient in more than a decade got infected, now that the outbreak has officially reached a fourth African country and everyone would very much like to know where it's heading next.

The patient in question is the Ugandan-born wife of a Swiss diplomat based in Abuja. According to the Swiss foreign ministry, she did not travel to the Democratic Republic of Congo, where the outbreak was first detected in mid-May before spreading to Uganda, Kenya and now Nigeria. Instead, the ministry said, she is believed to have contracted Ebola while travelling with her husband in Uganda. This contradicts earlier accounts from Uganda, which had said the woman travelled to eastern DR Congo - a discrepancy that will do absolutely nothing to soothe concerns about authorities' ability to contain an outbreak already billed as the most geographically widespread in history.

For the record, the Ugandan government reported Ebola cases in May and June before the WHO declared the country Ebola-free in August. A Ugandan government spokesperson told Reuters on Thursday that Uganda had no Ebola cases and that, if it did, it would make that information public - a statement that is either reassuring or slightly ominous, depending on your tolerance for official denials.

The World Health Organization says investigations are continuing to establish the likely source of infection. Meanwhile, the Africa Centres for Disease Control and Prevention is looking into whether the patient may have come into contact with an Ebola patient in Kenya, since both travelled from Uganda's Entebbe airport on 3 October, according to Dr Wessam Mankoula, head of emergency preparedness and response at the organisation.

Catherine Smallwood, a WHO Ebola incident manager in DR Congo, told a UN briefing in Geneva via video link on Friday that WHO staff in DR Congo had no information showing the Nigerian patient had travelled there. She said a link to the Kenya case was possible, but officials would need to compare the timing with when the Nigeria patient's symptoms began to determine whether infection more likely happened at the Ugandan airport or elsewhere.

Marion Koopmans, a Dutch virologist and member of the WHO's Ebola emergency committee, was considerably less convinced. "I think that is very speculative unless there is evidence of sharing the same space in a manner that could explain that," she said. "Random presence at the same location, a large airport, is not a supported epidemiological link by any standard of what we currently know." In other words: standing near someone in an airport terminal is not, technically, a transmission event.

Nigerian health minister Muhammad Ali Pate said the country's case remains contained and contact-tracing is continuing. "We are trying to contain it so it doesn't go out to the communities. Hopefully, it won't get to that and we are working hard to ensure that," Pate said. A sentiment shared by, one imagines, everyone.

Melaku Yirga, vice-president for Africa at Prosper Global (formerly Mercy Corps), said confirmation of Ebola in Kenya and Nigeria reinforces the need for countries to work closely together to prevent further transmission. "What matters most now is speed, sharing information across borders without delay and ensuring frontline health workers and local organisations have the resources to respond quickly," he said.

Ebola, for those fortunate enough not to have needed a refresher, is a highly contagious and often fatal viral disease affecting humans and non-human primates. It spreads through body fluids or contaminated materials and causes organ damage, blood vessel impairment and sometimes severe internal and external bleeding.

The current outbreak is caused by the rare Bundibugyo virus, which has no approved treatment or vaccine - a detail that manages to make everything above considerably less amusing. It was first announced on 15 May and has infected more than 9,500 people and killed nearly half of them. It is the largest and deadliest outbreak in DR Congo's history and second globally only to the 2014-16 west Africa outbreak, which infected more than 28,600 people and killed more than 11,000.

Reuters and the Associated Press contributed reporting.